Hydraulically controlled drive system



March 9, 1965 w. QUICK AL 3,172,264

HYDRAULICALLY CONTROLLED DRIVE SYSTEM Original Filed March 7, 1957 2Sheets-Sheet 1 FIG. 7

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N c5 I L MMv-s IMM a drive system with United States Patent 8 Claims.((11. 60-44) The present application is a divisional application of thecopending application Quick et al., Serial No. 644,516, filed March 7,1957, for Driving Systems for Machine Tools, issued on November 21,1961, as US. Patent No. 3,009,323.

The present invention relates to a hydraulically controlled drivesystem, and more particularly to a drive which includes fluid impellinginput means and turbine means having output means whose output torque isautomatically adjusted when the speed of a driven machine varies due toload fluctuations.

Certain machine tools are subjected to a variable load, but have to bedriven at an exactly constant speed. It is known to drive machines ofthis type by adjustable drive means, such as a Ward-Leonard drive, aninfinitely variable polyphase induction motor, or by a prime moverturning at constant speed and provided with an infinitely variablemechanical or hydraulic transmission.

These drives are expensive, and also the frequency of repair iscomparatively high. It is one object of the present invention toovercome disadvantages of known drives for maintaining a machine tool atconstant speed, and to provide a comparatively inexpensive hydraulicallycontrolled drive system serving this purpose.

Another object of the present invention is to provide atorque-converter, or a corresponding turbine-type drive withautomatically operating hydraulic means which regulate the drive to runat constant speed irrespective of the load, although the normalcharacteristic of such a drive would cause a speed reduction when theload is increased.

Another object of the present invention is to provide two control pumps,one of which rotates at constant speed, while the other rotates at thespeed of the driven shaft so that a pressure differential in a conduitconnecting the pumps indicates a speed variation of the driven shaft.

Another object of the present invention is to provide an automaticallyoperating control valve which automatically responds to very rapidaccelerations or decelerations of the output shaft to influence thehydraulic control system.

Another object of the invention is to provide the hydraulic controlsystem with a manually operated valve by which the control system can beset to different selected speeds of the output shaft.

With these objects in view, a drive system according to one embodimentof the invention comprises drive means, for example a torque converterwhose output torque can be adjusted by turning the impeller blades, afirst control pump which is driven at a selected constant speed, asecond control pump which is driven from the output means of the drivemeans, conduit means connecting the control pumps to each other so thata liquid is circulated through the conduit means, and pressureresponsive means communicating with the conduit and connected to theadjusting means of the torque converter.

When the second control pump runs at the desired speed of the controlledmachine, its output equals the 3,172,264 Patented Mar. 9, 1965 output ofthe first control pump which runs at constant speed. Consequently thereis no pressure differential created in the conduit means, and thepressure responsive means and the adjusting means are not actuated.

However, if the speed of the output shaft is reduced or increased due anincrease or reduction of the load torque, a pressure ditierential occursat the inlet and outlet of the second control pump, and such pressuredifferential actuates the pressure responsive means so that theadjusting means are operated to increase, or reduce, respectively theoutput torque of the torque converter until a condition of equilibriumis again obtained.

For example, if the cutting tool of a bar turning or peeling machineencounters greater resistance, the load torque is increased, and themachine will tend to slow down. However, since the output torque of thetorque converter is immediately increased, the additional load isovercome while the machine tool is adjusted to rotate at the desiredspeed.

In the preferred embodiment of the invention, a control conduit connectsthe outlet and the inlet of the first control pump which runs atconstant speed. Valve means are provided in the control conduit foradjusting the amount of liquid passing through the same, and thereby theamount of liquid supplied by the first control pump to the secondcontrol pump.

The output of the first control pump is chosen to be substantiallygreater than the output of the second control pump, and a manuallysettable valve means in the control conduit determines the amount ofliquid actually supplied by the first control pump to the second controlpump, so that the hydraulic control circuit can be set to a desiredselected speed of the output shaft which is then continuously andautomatically maintained during the operation.

An additional automatically operating valve is also located in thecontrol conduit, and is operated by the pressure in the conduit means toincrease or reduce the cross section of the control conduit whichprovides a by-pass for the liquid circulated by the first control pump.If the pressure differential varies in the main conduit means due toacceleration or deceleration of the driven shaft and of the secondcontrol pump, the automatic control valve is operated by the pressure toincrease the pressure further, or to reduce the pressure further so thata particularly fast adjusting action is obtained. In this manner, veryrapid accelerations and decelerations of the shaft are compensated, eventhough they may exist only for a very short time.

In the preferred embodiment of the invention, a pressure tank, areservoir, and a circulating pump are con nected to the main conduitmeans to prevent excessive pressure in the conduit means.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation together with additional objects and advantages there of, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing, inwhich:

FIG. 1 is a schematic view, partly in section, illustrating anembodiment of the invention; and

FIG. 2 is a longitudinal sectional view on an enlarged scale showing atorque converter used in the embodiment of FIG. 1.

Referring now to the drawings, a prime mover 83 drives through acoupling the input shaft 92 of a torque converter 84. As best seen inFIG. 2, a bushing or sleeve 93 is mounted on input shaft 92 for axialmovement, and has a pair of flanges 93' and 93" at one end, and ahelical gear 94 at the other end. A lever is turnably a mounted on thehousing by means of a pivot 91, and has a lower bifurcated arm providedwith a pair of slide members 95 which slidably engage the portion ofsleeve 93 between flanges 93 and 93". Consequently, by operation oflever 90, sleeve 93 can be shifted in axial direction as indicated bythe arrow 95. The helical gear 94 is in meshing engagement with helicalpinions 97 secured to shaft 97' which are mounted on a flange of inputshaft 92. The torque converter has stationary vanes 99, 100 and 101,between which vanes 102 and 103 of a turbine wheel 82a are located. Theturbine wheel is fixed on the output shaft 82. Impeller blades 98 aresecured to shaft 97', so that upon operation of lever 90 and shifting ofsleeve 93, the impeller blades 98 are turned to adjust the output torqueof the output means 82, 82a.

A piston rod 88 is connected by a pivot pin 89 to lever 90, and carriesa piston 85 located in a cylinder 86 which is pivotally mounted on apivot means 87. Conduits 105 and 106 are connected to the chambersformed by piston 85 in cylinder 86, and it is apparent that if liquid isapplied through conduit 105, piston 85 will move to the left, and thatwhen liquid is supplied through conduit 106, piston 85 will move to theright as viewed in FIG. 2, to effect a corresponding adjustment of theimpeller blades 98 to increase or decrease the output torque of shaft 82relative to the normal output torque obtained in an intermediateposition of piston 85.

FIG. 1 shows that conduits 105 and 106 are connected to a conduit means104 at two spaced points and 16. The inlet of a pump 107 is located inthe region of point 16 and its outlet is located in the region of point15. Pump 107 is driven from shaft 82 by a chain drive including chainwheels '110and111,and a chain 109. Consequently, pump 107 will rotate ata speed proportional to the speed of output shaft 82. Output shaft 82drives through a coupling the shaft 11 of a machine tool 10, so

that if the speed of output shaft 32 varies due to load variations ofmachine tool 10, pump 107 will rotate at correspondingly changed speeds.Consequently, the output of control pump 107 will be a measure of therotary speed of shaft 82 and 11. Another pump 108 is located in conduit104, and has an outlet pumping into part 17 of conduit 104 which isconnected to the inlet of pump 107. The inlet of pump 108 is connectedto conduit part 18 which leads to the outlet of pump 107.

Control pump 108 is driven through a coupling 115 from an electric motor112 which maintains pump 108 at a constant speed. The output of controlpump 108 is considerably higher than the output of control pump 107, forexample twice as high.

A control conduit 134 connects parts 17 and 18 of conduit 104 is formedwith a passage forming a portion of conduit part 17, and including aduct 132, another duct 133, and a chamber 30. Another duct 34 in valvebody 131 forms a portion of control conduit 134.

Duct 34 has a valve seat 33 in the region of chamber 36, and a needlevalve 31 cooperates with valve seat 33. Needle valve 31 is part of athreaded spindle 35 which can be operated by handwheel 135 so that theopen cross section of control conduit 134 can be' determined byoperation of needle valve 31 by handwheel 135. Means indicating variousspeeds may be provided in the region of handwheel 135, and assuming thatwheel 135 is set to a selected speed at which shaft 32 is to run, acertain cross section will be left free by needle valve 31 in controlconduit 134. Consequently not all the output of pump 108 will be pumpedto pump 107, but a part of the liquid will be recirculated throughconduit 134, and the amount and volume of this part of the liquid can beselected by setting valve 31.

Assuming that shaft 82' is to run at the desired speed, pump 107 willpump a volume corresponding to this desired speed. Pump 103 will pumpgreater volume, but

valve 31 is set to such a position that the same volume passes from-103to 107 as pump 107 is capable of pumping at the desired selectedspeed. Consequently as long as pump 107 runs at the desired speed, noliquid will be pumped into conduits 105 or 106, and piston will remainin its normal position. However, when pump 107 runs slower, or fastercorresponding to a deceleration or acceleration of shaft 82 due to aload variation, piston 85 will be shifted. For example, if the output ofpump 107 is increased, liquid will be pumped "through conduit intocylinder 86 and displace the piston to the left to elfect an adjustmentof the torque converter by which its output torque is reduced so thatthe speed drops again until the desired speed is again obtained.

If valve 31 is set to permit more liquid to pass from pump 108 to pump107, then pump 107 will have to run faster to obtain the condition ofequilibrium, corresponding to a difierent selected higher speed of shaft82.

In this manner, a desired speed of rotation of machine 10 is selected bysetting valve means 135, 35, 31.

In the above explanation of the operation of control pump 107, 108 andvalve 31, it was assumed that conduit 104 provides a closed circuit.However, to avoid excess pressure in conduit 104, under certainoperational conditions, a reservoir 119, a pressure tank 122, and acirculating pump 12 are provided. A conduit 117 with a check valve 118connects conduit part 118 with the reservoir 119. A conduit with a checkvalve 129 connects conduit part 17 with the reservoir 119. Consequently,when pump 107 rotates so fast that the amount of liquid pumped therebycannot be taken up by pump 103, liquid will pass through check valve 118and conduit 117 into the reservoir 119, while when pump 108 pumps toomuch liquid, the liquid will pass through check valve 129 and conduit130 into the reservoir 119. Circuilation pump 125 is driven by a motor124 to pump liquid from the reservoir 119 through conduit 120 intopressure tank 122 which contains air, and whose pres sure is indicatedby a manometer 123. A conduit 128 includes a check valve 121 andconnects pressure tank 122 with conduit part 18. Another conduit 126 hasa check valve 127 and connects pressure tank 122 with conduit part 17.If pump 108 sucks more liquid out of conduit portion 18 than pump 107can supply at the momentary speed of shaft '82, liquid is supplied fromprest sure tank 122 through conduit 128 and check valve 121-,

and conduit 126 in check valve 122 perform the corresponding functionfor conduit portions 17.

Valve body 131 has another duct 40 communicating with conduit part 17and opening into a cylinder space 41 which is vented at 42'. A piston138 is located in cylinder 41 and carries a valve member 137 whichprojects into the duct 34 of control conduit 134. A piston rod 139 isconnected to piston 138 and secured to a spring 140 whose tension can beadjusted by threaded spindle 142 carrying a handwheel 141. When pumps107 and 108 pump the same volume of liquid, spring 104 will hold valvemember 137 in a normal position. When the pressure in conduit portion 17becomes greater, the increased pressure in duct 40 and cylinder 41 willmove the valve member 137 to reduce the cross section of control conduit134. Consequently, less liquid can be recirculated through conduit 134to pump 108, and as a result, the pressure in conduit part 17 is furtherincreased,

. and even more liquid is pumped by pump 108 into conduit 106 to effecta displacement of piston 85 to the right. Even without valve member 137,piston 85 will be operated by a liquid pumped through conduit 106 bycontrol pump 108 if the speed of control pump 107 drops, but due to thefact that valve 137 becomes automatically effective to increasetheamount of liquid pumped by pump 108 into conduit 106, the adjustment'will be much faster so that a rapid acceleration of shafts 11, 82 willbe much faster compensated by the additional action of control valve137.

Of course, if shaft 82 runs too fast, and pump 107 pumps more liquidthan can be absorbed by pump 108, then this liquid will enter throughconduit 105 in the right chamber of cylinder 86 and displace piston 85to the left to reduce the output torque of shaft 82 under theseconditions, pump 107 will pump more liquid out of conduit part 17 thanpump 108 can supply, and consequently, the pressure in the cylinder 41will drop, and the force of spring 140 will prevail to retract valvemember 137 so that the cross section of control conduit 134 isincreased, and a greater amount of liquid can flow through controlconduit 134 back to pump 108. Pump 107 will receive even less liquidthrough conduit part 17, and will draw liquid through conduit 106 out ofthe left space in cylinder 86 whereby the adjustment of the torqueconverter is more rapidly effected as compared with an arrangementwithout control valve 137.

The pressure differential between points and 16 will determine the speedand direction of the control movement of piston 85, and as will beapparent from the above description of the operation of the controlpumps 107, 108, such pressure difierential will only occur when shaft 82runs faster, or slower, than a desired speed since otherwise controlpumps 107 and 108 pump equal amounts of liquid through conduit parts 17,18, so that no liquid is pumped through conduits 105 and 106. If shaft82 runs at an improper speed for such a time that one of the controlpumps produces an excess of liquid beyond the full capacity of cylinder86, one of the check valves 118 or 129 will open and excess liquid willflow into the reservoir 119 so that excess pressure in conduit 104 issafely prevented. In a corresponding manner, it one of the control pumpstends to create a vacuum in the conduit means 104, liquid will besupplied from the pressure tank 122 through one of the check valves 121and 127.

The drive system of the invention is operated in the following manner.First motor 112, which is either an asynchronous motor, or a synchronousmotor, is switched on and drives pump 108 which pumps liquid into conduit part 17. Since torque converter 84 and pump 107 are still at astandstill, the liquid pumped by pump 10% passes through conduit 106into the lefthand space of cylinder 86 and moves piston 85 all the wayto the right so that the torque converter is set to produce a maximumoutput torque, resulting in rapid acceleration of machine tool 10. Sincethe pressure in conduit part 17 is high, piston 138 will be displaced incylinder 41 and close control conduit 134. Excess pressure will beproduced in conduit part 17 when piston 85 is in its end position, sothat check valve 129 will open and control pump 108 will dischargethrough conduit 130 into reservoir 119. At the same time, liquid will besupplied from pressure tank 122 through conduit 128, check valve 121 andconduit part 18 to the inlet of control pump 108. Pump 125 maintains thepressure in tank 122, and provides the liquid from reservoir 119. Assoon as the prime mover motor 83 is switched on, torque converter willdrive machine tool 10 with the maximum output torque and accelerateshaft 82 so that pump 107 starts to operate at increasing speeds. Whencontrol pump 107 has reached such a speed that it pumps slightly moreliquid from conduit part 17 than is supplied by control pump .108 in theparticular position of valve 31, control pump 107 will pump liquid outof the lefthand space in cylinder 86 through conduit 106, and at thesame time pump liquid through conduit 105 into the righthand space ofcylinder 86, since more liquid is discharged by the outlet of pump 107than can be sucked in through conduit part 18 by the inlet of controlpump 108. Consequently, piston 85 moves from its end position at theright end of cylinder 86 toward its normal position, so that the outputtorque of torque converter 84 is reduced, resulting in a reduction ofthe speed of shaft 82, and consequently of control pump 107 until thedesired speed is obtained at which pump 107 and pump 108 pump the sameamount of liquid so that no pressure differential develops betweenpoints 15 and 16 of conduit means 104.

If during the operation load variations occur at machine tool 10, andthe speed of shaft 82 is reduced and increased, a pressure differentialwill develop at points 15 and 16, and piston 85 will be shifted toeffect a corresponding adjustment of the output torque of a torqueconverter. Whenever such pressure differential occurs, the pressure inconduit part 17 will either be increased, or decreased, and controlvalve 137 will immediately react to even further increase, or furtherdecrease the pressure differential between points 15 and 16, so thatpiston 85 will be more rapidly shifted than in an arrangement in whichcontrol valve 137 would not be provided.

From the above description of the hydraulic control system of thepresent invention, it will become apparent that the control pumps 107and 108 and control conduit 104 constitute a speed responsive controlmeans, while control valve 137 constitutes a control device which isresponsive to rapid acceleration or deceleration of the output shaft.

Although the drive system of the present invention has been described asdriving a machine tool, it will be appreciated that any machinesubjected to a variable load can be controlled to run at constant speedby the drive system of the invention.

It will be understood that each of the elements described above or twoor more together, may also find a useful application in other types ofdrive systems differing from the types described above.

While the invention has been illustrated and described as embodied in ahydraulically controlled drive system including a control pump runningat constant speed, and a control pump running at a speed of a shaftwhich is subjected to a variable load, it is not intended to be limitedto the details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

Without further analysis the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims. I

What is claimed and desired to be secured by Letters Patent is:

l. A drive system comprising, in combination, drive means includingoutput means and adjusting means for adjusting the output torque of saidoutput means; a shaft dr ven by said output means and adapted to drive amachine subjected to a variable load;.a first control pump; means fordriving said first control pump at a selected constant speed; a secondcontrol pump; means for driving said second control pump from saidshaft; conduit means connecting the outlet of said first control pumpwith the inlet of said second control pump and the outlet of said secondcontrol pump with the inlet of said first control pump whereby anoperating liquid is circulated through said conduit means so that thepressures at said inlet and outlet of said second control pump are equalwhen said shaft runs at a desired speed; and a pressure responsive meanshaving chamber means communicating with said conduit means at two pointslocated in the region of said inlet and outlet of said second controlpump, respectively, said pressure responsive means including a-movablecontrol element moving in opposite directions when the pressure at anyof said points exceeds the pressure at the other of said points, saidcontrol element being operatively connected to said adjusting means sothat said output means is adjusted to produce a greater or smalleroutput torque when a pressure differential at said points 3,1 I iscaused by a speed change of said shaft, and thereby of said secondcontrol pump, due to a load variation.

2. A drive system as set forth in claim 1 and including a pressure tankadapted to contain air; a reservoir; a circulation pump for pumping aliquid from said reservoir into said pressure tank; a first conduitconnecting the outlet of said first pump with said reservoir andincluding a check valve; a second conduit connecting the outlet of saidsecond control pump with said reservoir and including a check valve,said check valves permitting passage of liquid from said conduit meansinto said pressure tank; a third conduit connecting said pressure tankwith the inlet of said first control pump and including a check valveblocking passage of liquid into said pressure tank; and a fourth conduitconnecting said pressure tank with the inlet of said second control pumpand including a check. valve blocking passage of liquid into saidpressure tank.

3. A drive system comprising, in combination, drive means includingoutput means and adjusting means for adjusting theoutput torque of saidoutput means; a shaft driven by said output means and adapted to drive amachine subjected to a variable load; a first control pump; means fordriving said first control pump at a selected constant speed; a secondcontrol pump having a smaller output than said first control pump; meansfor driving said second control pump from said shaft; conduit meansconnecting the outlet of said first control pump with the inlet of saidsecond control pump and the outlet of said second control pump with theinlet of said first control pump whereby an operating liquid iscirculated through said'conduit means so that the pressures at saidinlet and outlet of said second control pump are equal when said shaftruns at a desired speed; a control conduit connecting the outlet and theinlet of said first control pump; manually settable valve means in saidcontrol conduit for adjusting the amount of liquid passing through thesame and thereby the amount of liquid supplied by said first controlpurnp to the inlet of said second control pump; and a pressureresponsive means having chamber means communicating with said conduitmeans at two points located in the region'of said inlet and outlet'ofsaid second control pump, respectively, said pressure responsive meansincluding a movable control element moving in opposite directions whenthe pressure at any of said points exceeds the pressure at the other ofsaid points, said'control element being operatively connected to saidadjusting means so that said output means is adjusted to produce agrea'ter'or smaller output torque when a pressure differential at saidpoints is caused by a speed change of said shaft, and thereby of saidsecond control pump, due to a load variation.

4. A drive system comprising, in combination, drive means includingoutput means and adjusting means for adjusting the output torque of saidoutput means; a shaft driven by said output means and adapted to drive amachine subjected to a variable load; a first control pump; means fordriving said first control pump at a selected constant speed; a secondcontrol pump having a smaller output than said first control pump; meansfor driving said second control pump from said shaft; conduitmeans-connecting the outlet-of said first control pump with the inlet ofsaid second control pump and the outlet of said second control pump withthe inlet of said first control pu'mpwhereby an operating liquid iscirculated through said conduit means so that the pressures at saidinlet and outlet of said second control pump are equal when said shaftruns at a desired speed; a control conduit connecting the outlet and theinlet of said first control pump; manually settable valve means in saidcontrol conduit for adjust ing the amount of liquid passing through thesame and thereby the amount of liquid supplied by said first controlpump to the inlet of said second control pump; hydraulically operatedcontrol valve means located in said control conduit communicating withsaid conduit means and controlled by the pressure in the same toautomatically increase or reduce the cross section of said controlconduit when the pressure in said conduit means is reduced or increased,respectively, whereby the pressure in said conduit means is furtherreduced or increased, respectively; and a pressure responsive meanshaving chamber means communicating with said conduit means at two pointslocated in the region of said inlet and outlet of said second controlpump, respectively, said pressure responsive means including a movablecontrol element moving in opposite directions when the pressure at anyof said points exceeds the pressure at the other of said points, saidcontrol element being operatively connected to said adjusting means sothat said output means is adjusted to produce a greater or smalleroutput torque when a pressure differential at said points is caused by aspeed change of said shaft, and thereby of said second control pump, dueto a load variation.

5. A drive system comprising, in combination, drive means includingoutput means and adjusting means for adjusting the output torque of saidoutput means; a shaft driven by said output means and adapted to drive amachine subjected to a variable load; a first control pump; means fordriving said first control pump at a selected constant speed; a secondcontrol pump; means for driving said second control pump from saidshaft; conduit means connecting the outlet of said first control pumpwith the inlet of said second control pump and the outlet of said secondcontrol pump with the inlet of said first control pump whereby anoperating liquid is circulated through said conduit means so that thepressures at said inlet and outlet of said second control pump are equalwhen said shaft runs at a desired speed; and a pressure responsive meansincluding a cylinder, a piston in said cylinder forming two chambersinsaid cylinder on opposite sides thereof, and two conduits respectivelyconnecting said chambers to two points of said conduit means located inthe region of said inlet and outlet-of said second control pump,

respectively, said piston moving in opposite directions when thepressure at any of said points exceeds the pressure at the other of saidpoints, said piston being operatively connected to said adjusting meansso that said output means is adjusted to produce a greater or smalleroutput torque when a pressure dififerential at said points is caused bya speed change of said shaft, and thereby of said second control pump,due to a load variation.

6. A drive system comprising, in combination, drive means includingoutput means and adjusting means for adjusting the output torque of saidoutput means; a shaft driven by said output means and adapted to drive amachine subjected to a variable load; a first control pump; means fordriving said first control pump at a selected constant speed; a secondcontrol pump having a smaller output than said first control pump; meansfor driving said second control pump from-said shaft; conduit meansconnecting the outlet of said first control pump with the inlet of saidsecond control pump and the outlet of said second control pump with theinlet of said first control pump whereby an operating liquid iscirculated through said conduit means so that the pressures at saidinlet and outlet of said second control pump are equal when said shaftruns at a desired speed; a control conduit connecting the outlet and theinlet of said first control pump; manually settable valve means in saidcontrol conduit for adjusting the amount of liquid passing-through thesame and thereby the amount of liquid supplied by said first controlpump to the inlet of said second control pump;-hydraulically operatedcontrol valve means located in said control conduit communicating withsaid conduit means and controlled by the pressure in the same toautomatically increase or reduce the cross section of said controlconduit when the pressure in said conduit means is reduced or increased,respectively, whereby the pressure in said conduit means is furtherreduced or increased; respectively; and a pressure responsive meansincluding a cylinder, a piston in said cylinder forming two-chambers insaid cylinder on opposite s'idesthereof, and two conduits'respectivelyconnecting said chambers to two points of said conduit means located inthe region of said inlet and outlet of said second control pump,respectively, said piston moving in opposite directions when thepressure at any of said points exceeds the pressure at the other of saidpoints, said piston being operatively connected to said adjusting meansso that said output means is adjusted to produce a greater or smalleroutput torque when a pressure ditferential at said points is caused by aspeed change of said shaft, and thereby of said second control pump, dueto a load variation.

7. A drive system comprising, in combination, prime mover means; drivemeans including fluid impelling input means driven by said prime movermeans, turbine means having rotary output means, and adjusting means forad justing the output torque of said output means; a shaft driven bysaid output means and adapted to drive a machine subjected to a variableload; a first control pump; means for driving said first control pump ata selected constant speed; a second control pump; means for driving saidsecond control pump from said shaft; conduit means connecting the outletof said first control pump with the inlet of said second control pumpand the outlet of said second control pump with the inlet of said firstcontrol pump whereby an operating liquid is circulated through saidconduit means so that the pressures at said inlet and outlet of saidsecond control pump are equal when said shaft runs at a desired speed; acontrol conduit connecting the outlet and the inlet of said firstcontrol pump; hydraulically operated control valve means located in saidcontrol conduit communicating with said conduit means and controlled bythe pressure in the, same to automatically increase or reduce the crosssection of said control conduit when the pressure in said conduit meansis reduced or increased, respectively, whereby the pressure in saidconduit means is further reduced or increased, respectively; and apressure responsive means having chamber means communicating with saidconduit means at two points located in the region of said inlet andoutlet of said second control pump, respectively, said pressureresponsive means including a movable control element moving in oppositedirections when the pressure at any of said points exceeds the pressureat the other of said points,

said control element being operatively connected to said adjusting meansso that said output means is adjusted to produce a greater or smalleroutput torque when a pressure diiferential at said points is caused by aspeed change of said shaft, and thereby of said second control pump, dueto a load variation.

8. A drive system comprising, in combination, prime mover means; drivemeans including fluid impelling input means driven by said prime movermeans, turbine means having rotary output means, and adjusting means foradjusting the output torque of said output means; a shaft driven by saidoutput means and adapted to drive a machine subjected to a variableload; a first control pump; means for driving said first control pump ata selected constant speed; a second control pump having a smaller outputthan said first control pump; means for driving said second control pumpfrom said shaft; conduit means connecting the outlet of said firstcontrol pump with the inlet of said second control pump and the outletof said second control pump with the inlet of said first control pumpwhereby an operating liquid is circulated through said conduit means sothat the pressures at said inlet and,

outlet of said second control pump are equal when said shaft runs at adesired speed; a control conduit connecting the outlet and the inlet ofsaid first control pump; manually settable valve means in said controlconduit for adjusting the amount of liquid passing through the same andthereby the amount of liquid supplied by said first control pump to theinlet of said second control pump; hydraulically operated control valvemeans located in said control conduit communicating with said conduitmeans and controlled by the pressure in the same to automaticallyincrease or reduce the cross section of said control conduit when thepressure in said conduit means is reduced or increased, respectively,whereby the pressure in said conduit means is further reduced orincreased, respectively; and a pressure responsive means including acylinder, a piston in said cylinder forming two chambers in saidcylinder on opposite sides thereof, and two conduits respectivelyconnecting said chambers to two points of said conduit means located inthe region of said inlet and outlet of said second control pump,respectively, said piston moving in opposite. directions when thepressure at any of said points exceeds the pressure at the other of saidpoints, said piston being operatively connected to said adjusting meansso that said output means is adjusted to produce a greater or smalleroutput torque when a pressure difierential at said'points is caused by aspeed change of said shaft, and thereby of said second control pump, dueto a load variation.

References Cited in the file of this patent UNITED STATES PATENTS

1. A DRIVE SYSTEM COMPRISING, IN COMBINATION, DRIVE MEANS INCLUDINGOUTPUT MEANS AND ADJUSTING MEANS FOR ADJUSTING THE OUTPUT TORQUE OF SAIDOUTPUT MEANS; A SHAFT DRIVEN BY SAID OUTPUT MEANS AND ADAPTED TO DRIVE AMACHINE SUBJECTED TO A VARIABLE LOAD; A FIRSTR CONTROL PUMP; MEANS FORDRIVING SAID FIRST CONTROL PUMP AT A SELECTED CONSTANT SPEED; A SECONDCONTROL PUMP; MEANS FOR DRIVING SAID SECOND CONTROL PUMP FROM SAIDSHAFT; CONDUIT MEANS CONNECTING THE OUTLET OF SAID FIRST CONTROL PUMPWITH THE INLET OF SAID SECOND CONTROL PUMP AND THE OUTLET OF SAID SECONDCONTROL PUMP WITH THE INLET OF SAID FIRST CONTROL PUMP WHEREBY ANOPERATING LIQUID IS CIRCULATED THROUGH SAID CONDUIT MENS SO THAT THEPRESSURES AT SAID INLET AND OUTLET OF SAID SECOND CONTROL PUMP ARE EQUALWHEN SAID SHAFT RUNS AT A DESIRED SPEED; AND A PRESSURE RESPONSIVE MEANSHAVING CHAMBER MEANS COMMUNICATING WITH SAID CONDUIT MEANS AT TWO POINTSLOCATED IN THE REGION OF SAID INLET AND OUTLET OF SAID SECOND CONTROLPUMP, RESPECTIVELY, SAID PRESSURE RESPONSIVE MEANS INCLUDING A MOVABLECONTROL ELEMENT MOVING IN OPPOSITE DIRECTIONS WHEN THE PRESSURE AT ANYOF SAID POINTS EXCEEDS THE PRESSURE AT THE OTHER OF SAID POINTS, SAIDCONTROL ELEMENT BEING OPERATIVELY CONNECTED TO SAID ADJUSTING MEANS SOTHAT SAID OUTPUT MEANS IS ADJUSTED TO PRODUCE A GREATER OR SMALLEROUTPUT TORQUE WHEN A PRESSURE DIFFERENTIAL AT SAID POINTS IS CAUSED BY ASPEED CHANGE OF SAID SHAFT, AND THEREBY OF SAID SECOND CONTROL PUMP, DUETO A LOAD VARIATION.